1. Field of the Invention
The present invention relates to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of handling a transmission in an unlicensed band in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) (e.g., using LTE), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-1X standard or later versions.
Network operators propose to offload network traffic of the LTE/LTE-A system to an unlicensed band, to ease load of the network traffic. For example, the eNB may provide services to the UE via both a licensed band and the unlicensed band. However, even if the UE is scheduled by the eNB to perform a UL transmission at a first time instant in the unlicensed band, the UE may not be able to complete the UL transmission due to uncertainty of available resource of the unlicensed band. That is, there may not be available resource (i.e., clean channel) for performing the UL transmission. For example, the resource of the unlicensed band may be occupied by another communication device operating a different communication standard (e.g., IEEE 802.11). Accordingly, communication operations between the UE and the eNB is affected, and throughput of the UE is degraded. Benefit of introduction of the unlicensed band is reduced. Thus, how to handle a transmission in the unlicensed band is an important problem to be solved.